This invention relates generally to tools used in downhole environment. More specifically, this invention relates to deploying and retrieving tool sections of a tool string through well surface equipment, with connection and disconnection of the tool sections occurring in a portion of the well surface equipment that is isolated from wellhead pressure.
In deploying tools in a wellbore, the tools are usually assembled into a relatively long string, with the string run into the wellbore. In one example, the string is a perforating string having a number of perforating guns attached in series, along with other components.
For efficient assembly and disassembly of a tool string, well surface equipment is provided to maintain the wellbore under pressure while tool sections are being connected and disconnected. One such well surface equipment is the Completions Insertion and Retrieval under Pressure (CIRP) system made by Schlumberger Technology Corporation. In the CIRP system, a connector assembly that cooperates with rams in the well surface equipment is used for connecting and disconnecting tool sections while the wellbore is maintained at pressure. The CIRP system allows wellbore pressure to be maintained up to around 7,000 psi while still allowing assembly and disassembly of tool string sections at the well surface.
In some applications, it may be desirable to further increase the wellbore pressure at the wellhead. At some point, however, the increased pressure at the wellhead makes it difficult to manipulate a tool section in the well surface equipment. This is due to the fact that an operator has to control the tool section in the presence of an upward force provided by the wellhead pressure. As a result, in applications with elevated wellhead pressure (e.g., greater than 7,000 psi), assembly and disassembly of a tool string at the wellhead can be difficult.
For example, if coiled tubing is used to deploy a tool section, the force required to move the tool section and overcome the wellhead pressure can be so high that the operator cannot control the tool section sufficiently to conduct precise connection operations. For instance, a typical 1.75 inch diameter coiled tubing has approximately a 2.4 square inch cross-sectional surface area. If the wellhead is pressurized to 10,000 psi, the operator would have to apply at least 24,000 pounds of force to move the tool section, which makes precise operations very difficult.
In general, an improved method and apparatus is provided to isolate a portion of the well surface equipment to enable easier assembly or disassembly of a tool string at the wellhead. For example, a method of deploying a tool string includes inserting a first tool into a wellbore through well surface equipment, the wellbore being at an elevated pressure, and isolating a first portion of the well surface equipment from the elevated wellbore pressure. A second tool is connected to the first tool in the portion of the well surface equipment that is isolated from the elevated wellbore pressure, the first tool and second tool making up at least part of the tool string. The tool string has an inner bore, and the inner bore is opened to fluid communication in response to activation of the tool string, such as by detonation of an explosive detonating cord. A barrier mechanism is provided in the tool string to block one portion of the inner bore from another portion of the inner bore to maintain isolation of the first portion of the well surface equipment even after activation of the tool string.
Other or alternative features will be apparent from the following description, from the drawings, and from the claims.